Transmission assemblies for hybrid motor vehicles are known comprising two clutches and an electrical machine, arranged between the internal combustion engine of the vehicle and its gearbox. An assembly of this type is described for example in document FR 2 830 589. Each of the clutches comprises a friction disc, a clutch stop, a reaction plate, and a clutch mechanism, comprising a pressure plate which is fitted such as to be mobile axially relative to the said reaction plate, between an engaged position in which the friction disc is gripped between the said pressure and reaction plates, and a released position. The two clutches are arranged on both sides of the electrical machine. The mechanism of a first clutch, which is arranged on the engine side, is configured to be associated with the crankshaft of the internal combustion engine. The friction disc of the first clutch is fitted integrally in rotation with an intermediate shaft which is secured on a hub for support of the rotor of the electrical machine. The mechanism, as well as the reaction plate of the second clutch, arranged on the gearbox side, are fitted integrally in rotation with the said hub for support of the rotor, and the friction disc of the said second clutch is designed to co-operate with an input shaft of a gearbox.
The clutch on the engine side thus makes it possible to couple the crankshaft of the combustion engine in rotation with the rotor of the electrical machine, and the clutch on the gearbox side makes it possible to couple the rotor with the input shaft of the gearbox. Thus, it is possible to cut off the internal combustion engine at each stoppage, and to restart it by means of the electrical machine. The electrical machine can also constitute an electric brake, or supply additional energy to the combustion engine in order to assist it, or prevent it from stalling. When the engine is running, the electrical machine acts as an alternator.
The reaction plate of the clutch on the gearbox side is placed at an axial distance from the electrical machine, in order to limit the magnetic disturbances. However, on the other hand, dust or particles, produced in particular by the rubbing of the friction disc of the clutch on its respective pressure and reaction plates during clutch operations, are liable to access the air gap of the electrical machine. This dust is liable to damage the electrical machine and detract from its performance.